1. Field of the Invention
The present invention relates to an image forming apparatus which develops image of high-definition with liquid developer.
2. Description of Related Art
Heretofore, image forming apparatus using liquid developer generally use the method of causing electrical migration of toner fine particles which are dispersed in an insulating liquid carrier such as aliphatic saturated hydrocarbon and the like, so that the toner fine particles adhere to the surface of a dielectric body on which an electrostatic latent image is formed. This method enables the use of toner particles with smaller diameter than powder toner which is used in a developing device, and it is suitable for producing an image of a high resolution. There is also an advantage that liquid toner needs less energy for fixing than powder toner. However, aliphatic saturated hydrocarbon used as liquid carrier generates a disagreeable smell, which is unsuitable for the use in offices and homes. On the other hand, an image forming apparatus using liquid developer with water as the main ingredient is proposed in Japanese patent publication No. Sho 52-6091, Hei 1-40985, and Japanese patent application laid-open No. Sho 62-5282 respectively. Such the image forming apparatus, using the aqueous liquid developer, can resolve the problem concerning smell and reduce the cost of developer material.
However, in the image forming apparatus described in Japanese patent publication No. Sho 52-6091, a developer retainer is formed with a spirally arranged groove which holds therein liquid developer, which will adhere to a sheet on which an electrostatic latent image is formed. In this apparatus, the resolution varies depending on the pitch of the spiral groove, so that a high-resolution can not be obtained. Specifically, the liquid developer, which selectively adheres to a latent image formed portion on a sheet, is held in the spiral groove, resulting in the difficulty in the separation of the liquid developer in the grooved direction and thus deteriorating the resolution in the grooved direction. The groove of the developer retainer is formed by a mechanical cutting process, which is hard to make a groove having a width of 0.1 mm or less. This sets a limit in the resolution in the direction of a groove width.
In the development apparatus described in the Japanese patent publication No. Hei 1-40985 and Japanese patent application laid-open No. Sho 62-5282, the developer retainer, or a sleeve with many fine bores for holding developer is placed close to an image bearing member (photosensitive drum) but without making contact therewith, and the liquid developer held in the sleeve is jumped up by the electrostatic force to the image bearing member, the latent image formed on the image bearing member is developed into a visual image. Since the electric field of the electrostatic latent image abruptly becomes flatter with distance from the surface of the image bearing member, the clearance between the image bearing member and the sleeve is required to be several tens .mu.m or less. Such the minute clearance is difficult to be precisely maintained at a constant distance. Variation in the clearance distance will causes a change in the electrostatic force, resulting in a deterioration of image quality.